(Warning: This post contains spoilers for the midseason finale of “This Is Us.”)

Griffin Dunne has joined the cast of “This Is Us” in a key recurring role for the back half of Season 3: Jack Pearson’s long-presumed-dead little brother, Nicky.

The actor will play an older version of the Pearson family member — who was revealed to have survived the Vietnam War on the show’s fall finale Tuesday night — when the drama returns at midseason, an NBC spokesperson tells TheWrap.

During the closing moments of tonight’s episode of “This Is Us,” we briefly see an out-of-focus, older version of Nicky (played by Dunne), living in a trailer in Bradford, Pennsylvania — as indicated by a well-placed piece of mail.

The younger Nicky — first introduced to fans in Episode 304, “Vietnam” — is portrayed by Michael Angarano.

You can find out more about this shocking revelation on the Dan Fogelman-created series’ midseason finale here — and the identity of Future Tess and Future Randall’s “her” here.